🟡 Senior's Tip: Nuclear Physics is the final chapter and a favourite for 1 AMU question on α/β/γ properties, half-life, fission vs fusion, or mass-energy equivalence. The α-β-γ comparison table is GOLD — memorise it cold. Half-life numericals are easy if you practice. Fission vs fusion differences are frequently tested. Let's master every concept!
1) Discovery and Structure of the Nucleus
The atom consists of a tiny, dense, positively charged nucleus surrounded by negatively charged electrons. The nucleus was discovered by Ernest Rutherford in 1911 through his famous gold foil experiment (α-particle scattering experiment).
🟡 Rutherford's Gold Foil Experiment — Key Results:
• Most α-particles passed straight through the gold foil (atoms are mostly empty space)
• Some α-particles were deflected at small angles (positive charge of nucleus repels α-particles)
• A very few (1 in 8000) bounced back (direct hit with the tiny, dense, positively charged nucleus)
• Conclusion: Atom has a small, dense, positively charged centre called the nucleus
• Most α-particles passed straight through the gold foil (atoms are mostly empty space)
• Some α-particles were deflected at small angles (positive charge of nucleus repels α-particles)
• A very few (1 in 8000) bounced back (direct hit with the tiny, dense, positively charged nucleus)
• Conclusion: Atom has a small, dense, positively charged centre called the nucleus
Composition of the nucleus:
Nucleus = Protons (p⁺) + Neutrons (n⁰) = Nucleons
Atomic number (Z) = number of protons
Mass number (A) = number of protons + number of neutrons
Neutron number (N) = A − Z
Notation: ᴬ₂X (e.g., ²³⁵₉₂U)
🟡 Nuclear Size and Density:
• Nuclear size: ~10⁻¹⁵ m (1 femtometre = 1 fm). For comparison, atom size is ~10⁻¹⁰ m
• Nuclear radius: R = R₀A¹/³ where R₀ ≈ 1.2 × 10⁻¹⁵ m
• Nuclear density: approximately 2.3 × 10¹⁷ kg/m³ — EXTREMELY high!
• A sugar-cube sized piece of nuclear matter would weigh ~200 million tons!
• Density is approximately independent of mass number A (nucleons are tightly packed)
• Nuclear size: ~10⁻¹⁵ m (1 femtometre = 1 fm). For comparison, atom size is ~10⁻¹⁰ m
• Nuclear radius: R = R₀A¹/³ where R₀ ≈ 1.2 × 10⁻¹⁵ m
• Nuclear density: approximately 2.3 × 10¹⁷ kg/m³ — EXTREMELY high!
• A sugar-cube sized piece of nuclear matter would weigh ~200 million tons!
• Density is approximately independent of mass number A (nucleons are tightly packed)
🔥 AMU PYQ: The nucleus of an atom consists of:
(A) Protons only (B) Neutrons only (C) Protons and neutrons (D) Protons and electrons
Ans: C (protons + neutrons = nucleons)
(A) Protons only (B) Neutrons only (C) Protons and neutrons (D) Protons and electrons
Ans: C (protons + neutrons = nucleons)
2) Radioactivity — Discovery and Types ⭐
Radioactivity is the spontaneous emission of radiation from the nucleus of an unstable atom. It was discovered by Henri Becquerel in 1896 when he noticed that uranium salts could fog a photographic plate even in darkness. Later, Marie and Pierre Curie isolated polonium and radium — highly radioactive elements.
Key characteristics of radioactivity:
• It is a spontaneous process — cannot be controlled or stopped
• It is a nuclear phenomenon — the nucleus decays, not the electrons
• It is random — we cannot predict which atom will decay next
• It is statistical — but predictable for large numbers of atoms
• Unaffected by temperature, pressure, chemical reactions
• Three types of radiation are emitted: α (alpha), β (beta), γ (gamma)
• It is a spontaneous process — cannot be controlled or stopped
• It is a nuclear phenomenon — the nucleus decays, not the electrons
• It is random — we cannot predict which atom will decay next
• It is statistical — but predictable for large numbers of atoms
• Unaffected by temperature, pressure, chemical reactions
• Three types of radiation are emitted: α (alpha), β (beta), γ (gamma)
🔥 AMU PYQ: Radioactivity was discovered by:
(A) Rutherford (B) Becquerel (C) Curie (D) Fermi
Ans: B (Henri Becquerel, 1896)
(A) Rutherford (B) Becquerel (C) Curie (D) Fermi
Ans: B (Henri Becquerel, 1896)
Types of Radioactive Radiation — COMPARISON TABLE:
| Property | α (Alpha) | β (Beta) | γ (Gamma) |
|---|---|---|---|
| Nature | Helium nucleus (⁴₂He²⁺) | Fast electron (₋₁⁰e⁻) or positron (₊₁⁰e⁺) | High-energy EM wave (photon) |
| Symbol | α, ⁴₂He | β⁻, ₋₁⁰e / β⁺, ₊₁⁰e | γ |
| Charge | +2e | −e (β⁻) or +e (β⁺) | 0 (neutral) |
| Mass | 4 amu (~6.64×10⁻²⁷ kg) | ~0.00055 amu (same as electron) | 0 (rest mass) |
| Speed | ~1/10th of speed of light (slowest) | ~9/10th of speed of light (very fast) | Speed of light c (fastest) |
| Ionising power | HIGHEST (heavy, slow → causes maximum ionisation) | Moderate | LOWEST (weak interaction with matter) |
| Penetrating power | LOWEST — stopped by paper / few cm of air | Moderate — stopped by 5 mm aluminum sheet | HIGHEST — stopped by thick lead / concrete |
| Deflection in E-field | Deflected towards negative plate (+2 charge) | Deflected towards positive plate (−1 charge) | Not deflected (no charge) |
| Deflection in B-field | Deflected (opposite to β direction) | Deflected (opposite to α direction) | Not deflected (no charge) |
| Effect on A/Z | A decreases by 4, Z decreases by 2 | A unchanged, Z increases by 1 (β⁻) / Z decreases by 1 (β⁺) | No change in A or Z |
| Examples | ²³⁸₉₂U → ²³⁴₉₀Th + α | ²³⁴₉₀Th → ²³⁴₉₁Pa + β⁻ | Co-60* → Co-60 + γ (excited → ground state) |
🟡 Senior's Tip — Memorise the α-β-γ Table with this pattern:
• α: Most ionising, Least penetrating (like a heavy truck — it smashes into everything but can't go far)
• γ: Least ionising, Most penetrating (like a bullet train — it's high energy and can go through a lot)
• β: Moderate in both (middle child)
• α deflects toward −ve plate, β toward +ve plate, γ not deflected at all
• In magnetic field: α and β deflect in opposite directions (using Fleming's left-hand rule for moving charges)
• α: Most ionising, Least penetrating (like a heavy truck — it smashes into everything but can't go far)
• γ: Least ionising, Most penetrating (like a bullet train — it's high energy and can go through a lot)
• β: Moderate in both (middle child)
• α deflects toward −ve plate, β toward +ve plate, γ not deflected at all
• In magnetic field: α and β deflect in opposite directions (using Fleming's left-hand rule for moving charges)
🔥 AMU PYQ: Which radiation has the highest penetrating power?
(A) Alpha (B) Beta (C) Gamma (D) All equal
Ans: C (gamma rays are the most penetrating)
(A) Alpha (B) Beta (C) Gamma (D) All equal
Ans: C (gamma rays are the most penetrating)
🔥 AMU PYQ: Which radiation has the highest ionising power?
(A) Alpha (B) Beta (C) Gamma (D) Neutron
Ans: A (alpha particles are heaviest → maximum ionisation)
(A) Alpha (B) Beta (C) Gamma (D) Neutron
Ans: A (alpha particles are heaviest → maximum ionisation)
🔥 AMU PYQ: In a magnetic field, gamma rays:
(A) Deflect towards north (B) Deflect towards south (C) Are not deflected (D) Curve in a circle
Ans: C (gamma = EM wave, no charge, no deflection)
(A) Deflect towards north (B) Deflect towards south (C) Are not deflected (D) Curve in a circle
Ans: C (gamma = EM wave, no charge, no deflection)
🔥 AMU PYQ: Alpha particles are:
(A) Electrons (B) Protons (C) Helium nuclei (D) Neutrons
Ans: C (alpha = 2 protons + 2 neutrons = helium nucleus)
(A) Electrons (B) Protons (C) Helium nuclei (D) Neutrons
Ans: C (alpha = 2 protons + 2 neutrons = helium nucleus)
🔥 AMU PYQ: Which of the following is NOT a type of radioactive radiation?
(A) Alpha (B) Beta (C) Gamma (D) Delta
Ans: D (α, β, γ are the three types)
(A) Alpha (B) Beta (C) Gamma (D) Delta
Ans: D (α, β, γ are the three types)
3) Soddy-Fajans Displacement Laws — NEW
These laws describe what happens to the nucleus when it emits α, β, or γ radiation.
Soddy-Fajans Displacement Laws:
1. α-decay: When a nucleus emits an α-particle (⁴₂He), its mass number decreases by 4 and atomic number decreases by 2.
Example: ²³⁸₉₂U → ²³⁴₉₀Th + α
2. β⁻-decay: When a nucleus emits a β⁻ particle (₋₁⁰e), its mass number remains same, atomic number increases by 1.
Example: ²³⁴₉₀Th → ²³⁴₉₁Pa + β⁻ (a neutron converts to proton + electron + antineutrino)
3. γ-decay: When an excited nucleus emits a γ photon, there is NO change in mass number or atomic number.
The * indicates the nucleus is in an excited (higher energy) state.
1. α-decay: When a nucleus emits an α-particle (⁴₂He), its mass number decreases by 4 and atomic number decreases by 2.
ᴬ₂X → ᴬ⁻⁴₂₋₂Y + α (⁴₂He)Example: ²³⁸₉₂U → ²³⁴₉₀Th + α
2. β⁻-decay: When a nucleus emits a β⁻ particle (₋₁⁰e), its mass number remains same, atomic number increases by 1.
ᴬ₂X → ᴬ₂₊₁Y + β⁻ + ν̄ₑExample: ²³⁴₉₀Th → ²³⁴₉₁Pa + β⁻ (a neutron converts to proton + electron + antineutrino)
3. γ-decay: When an excited nucleus emits a γ photon, there is NO change in mass number or atomic number.
ᴬ₂X* → ᴬ₂X + γThe * indicates the nucleus is in an excited (higher energy) state.
🟡 Remember:
• α-decay: A−4, Z−2 (both go DOWN)
• β⁻-decay: A same, Z+1 (Z goes UP)
• β⁺-decay: A same, Z−1 (Z goes down — positron emission)
• γ-decay: No change in A or Z (just energy release)
• α-decay: A−4, Z−2 (both go DOWN)
• β⁻-decay: A same, Z+1 (Z goes UP)
• β⁺-decay: A same, Z−1 (Z goes down — positron emission)
• γ-decay: No change in A or Z (just energy release)
Numerical: A radioactive nucleus ²²⁶₈₈Ra undergoes α-decay. Find the daughter nucleus.
Solution:
Ra (Z=88, A=226) → α-decay → A' = 226−4 = 222, Z' = 88−2 = 86
Element with Z=86 is Radon (Rn). So: ²²⁶₈₈Ra → ²²²₈₆Rn + α (Radon-222)
Solution:
Ra (Z=88, A=226) → α-decay → A' = 226−4 = 222, Z' = 88−2 = 86
Element with Z=86 is Radon (Rn). So: ²²⁶₈₈Ra → ²²²₈₆Rn + α (Radon-222)
Numerical: ²¹⁴₈₂Pb undergoes β⁻-decay. Find the daughter.
Solution:
β⁻-decay: A' = 214 (same), Z' = 82+1 = 83
Element with Z=83 is Bismuth (Bi). So: ²¹⁴₈₂Pb → ²¹⁴₈₃Bi + β⁻ (Bismuth-214)
Solution:
β⁻-decay: A' = 214 (same), Z' = 82+1 = 83
Element with Z=83 is Bismuth (Bi). So: ²¹⁴₈₂Pb → ²¹⁴₈₃Bi + β⁻ (Bismuth-214)
4) Radioactive Decay Law and Half-Life ⭐
The radioactive decay law states that the number of atoms decaying per unit time is proportional to the number of atoms present. This gives us an exponential decay curve.
Radioactive Decay Law:
N = N₀ × e^(−λt)
N₀ = initial number of atoms
N = number of atoms remaining after time t
λ = decay constant (s⁻¹)
t = time
Half-Life (T₁/₂):
The time taken for half the atoms in a radioactive sample to decay.
Relation:
Mean Life (τ): Average lifetime of a radioactive atom
The time taken for half the atoms in a radioactive sample to decay.
T₁/₂ = ln(2) / λ = 0.693 / λ
Relation:
N = N₀ × (½)ⁿ where n = t / T₁/₂Mean Life (τ): Average lifetime of a radioactive atom
τ = 1 / λ = 1.44 × T₁/₂
🟡 How Half-Life Works — Step by Step:
• Initially: 100% (N₀ atoms)
• After 1 half-life: 50% remains (N₀/2)
• After 2 half-lives: 25% remains (N₀/4)
• After 3 half-lives: 12.5% remains (N₀/8)
• After n half-lives: (½)ⁿ × 100% remains
Formula: N = N₀ × (½)^(t/T₁/₂)
• Initially: 100% (N₀ atoms)
• After 1 half-life: 50% remains (N₀/2)
• After 2 half-lives: 25% remains (N₀/4)
• After 3 half-lives: 12.5% remains (N₀/8)
• After n half-lives: (½)ⁿ × 100% remains
Formula: N = N₀ × (½)^(t/T₁/₂)
Numerical 1 — Basic Half-Life: The half-life of a radioactive substance is 10 days. What fraction remains after 30 days?
Solution:
n = t/T₁/₂ = 30/10 = 3 half-lives
Remaining fraction = (½)³ = 1/8 = 0.125 or 12.5%
Solution:
n = t/T₁/₂ = 30/10 = 3 half-lives
Remaining fraction = (½)³ = 1/8 = 0.125 or 12.5%
Numerical 2 — Finding Half-Life: A radioactive sample reduces from 100 g to 12.5 g in 30 days. Find its half-life.
Solution:
100 → 50 → 25 → 12.5 (three half-lives to go from 100 to 12.5)
3 half-lives = 30 days → T₁/₂ = 30/3 = 10 days
Solution:
100 → 50 → 25 → 12.5 (three half-lives to go from 100 to 12.5)
3 half-lives = 30 days → T₁/₂ = 30/3 = 10 days
Numerical 3 — Mass Remaining: The half-life of I-131 is 8 days. If we start with 40 g, how much remains after 24 days?
Solution:
n = 24/8 = 3 half-lives
Mass remaining = 40 × (½)³ = 40 × 1/8 = 5 g
Solution:
n = 24/8 = 3 half-lives
Mass remaining = 40 × (½)³ = 40 × 1/8 = 5 g
Numerical 4 — Advanced: The half-life of C-14 is 5730 years. A fossil has 1/16 of the original C-14. How old is it?
Solution:
N/N₀ = 1/16 = (½)⁴ → n = 4 half-lives
Age = n × T₁/₂ = 4 × 5730 = 22,920 years
Solution:
N/N₀ = 1/16 = (½)⁴ → n = 4 half-lives
Age = n × T₁/₂ = 4 × 5730 = 22,920 years
🔥 AMU PYQ: If the half-life of a substance is 5 days, what fraction remains after 15 days?
Ans: 15 days = 3 half-lives → remaining = (½)³ = 1/8
Ans: 15 days = 3 half-lives → remaining = (½)³ = 1/8
🔥 AMU PYQ: The half-life of a radioactive sample is 10 days. After 30 days, the remaining fraction is:
Ans: 30/10 = 3 half-lives → (½)³ = 1/8
Ans: 30/10 = 3 half-lives → (½)³ = 1/8
5) Radioactive Series — NEW
When a radioactive nucleus decays, the daughter nucleus may also be radioactive. This leads to a radioactive decay series (also called a decay chain) — a sequence of successive decays until a stable nucleus is reached.
Major Radioactive Series:
1. Uranium Series (4n+2):
²³⁸₉₂U → [14 decays: 8α + 6β⁻] → ²⁰⁶₈₂Pb (stable)
2. Thorium Series (4n):
²³²₉₀Th → [10 decays: 6α + 4β⁻] → ²⁰⁸₈₂Pb (stable)
3. Actinium Series (4n+3):
²³⁵₉₂U → [11 decays: 7α + 4β⁻] → ²⁰⁷₈₂Pb (stable)
All three end in stable isotopes of LEAD (Pb)!
1. Uranium Series (4n+2):
²³⁸₉₂U → [14 decays: 8α + 6β⁻] → ²⁰⁶₈₂Pb (stable)
2. Thorium Series (4n):
²³²₉₀Th → [10 decays: 6α + 4β⁻] → ²⁰⁸₈₂Pb (stable)
3. Actinium Series (4n+3):
²³⁵₉₂U → [11 decays: 7α + 4β⁻] → ²⁰⁷₈₂Pb (stable)
All three end in stable isotopes of LEAD (Pb)!
6) Artificial (Induced) Radioactivity — NEW
Natural radioactivity occurs spontaneously. But radioactivity can also be induced by bombarding stable nuclei with particles (α, p, n, etc.).
Key Experiments:
1. Rutherford (1919): First artificial transmutation
¹⁴₇N + α (⁴₂He) → ¹⁷₈O + ¹₁p
(Nitrogen bombarded with alpha particles → Oxygen + proton)
2. Fermi (1934): Neutron bombardment
Bombarding uranium with neutrons led to the discovery of nuclear fission
²³⁵₉₂U + n → [fission fragments] + neutrons + energy
1. Rutherford (1919): First artificial transmutation
¹⁴₇N + α (⁴₂He) → ¹⁷₈O + ¹₁p
(Nitrogen bombarded with alpha particles → Oxygen + proton)
2. Fermi (1934): Neutron bombardment
Bombarding uranium with neutrons led to the discovery of nuclear fission
²³⁵₉₂U + n → [fission fragments] + neutrons + energy
7) Mass Defect and Binding Energy ⭐
This is one of the most important concepts in nuclear physics. When protons and neutrons combine to form a nucleus, the mass of the nucleus is less than the sum of masses of individual nucleons. This "missing mass" is called the mass defect, and it is converted into binding energy that holds the nucleus together.
Mass Defect (Δm):
Δm = [Z × m_p + N × m_n] − M_nucleus
m_p = mass of proton = 1.007276 u
m_n = mass of neutron = 1.008665 u
M_nucleus = actual mass of nucleus
1 u (amu) = 1.66 × 10⁻²⁷ kg
Binding Energy (BE):
Binding Energy Per Nucleon:
This tells us how tightly bound a nucleus is. Higher BE/A = more stable nucleus.
BE = Δm × c²
Energy equivalent of 1 u = 931.5 MeV
BE (in MeV) = Δm (in u) × 931.5
Binding Energy Per Nucleon:
BE/A = Total Binding Energy / Mass Number
This tells us how tightly bound a nucleus is. Higher BE/A = more stable nucleus.
🟡 BE/A vs Mass Number Graph — THE MOST IMPORTANT GRAPH:
• BE/A increases sharply for light nuclei, peaks at Fe-56 (~8.8 MeV/nucleon) — the most stable nucleus
• BE/A then slowly decreases for heavier nuclei
• Nuclear fission: Heavy nuclei (like U-235) → split into medium-mass nuclei → increase in BE/A → energy released
• Nuclear fusion: Light nuclei (like H-1, H-2) → combine into heavier nucleus → increase in BE/A → energy released
• Both fission and fusion move towards Fe-56 (the maximum stability), releasing energy
• BE/A increases sharply for light nuclei, peaks at Fe-56 (~8.8 MeV/nucleon) — the most stable nucleus
• BE/A then slowly decreases for heavier nuclei
• Nuclear fission: Heavy nuclei (like U-235) → split into medium-mass nuclei → increase in BE/A → energy released
• Nuclear fusion: Light nuclei (like H-1, H-2) → combine into heavier nucleus → increase in BE/A → energy released
• Both fission and fusion move towards Fe-56 (the maximum stability), releasing energy
Numerical 1 — Mass Defect of Helium:
Given: m_p = 1.007276 u, m_n = 1.008665 u, mass of ⁴₂He = 4.001506 u
Find mass defect and binding energy.
Solution:
He has Z=2 (2 protons), N=2 (2 neutrons)
Total mass of constituents = 2(1.007276) + 2(1.008665) = 2.014552 + 2.017330 = 4.031882 u
Δm = 4.031882 − 4.001506 = 0.030376 u
BE = 0.030376 × 931.5 = 28.3 MeV
BE/A = 28.3/4 = 7.07 MeV/nucleon
Given: m_p = 1.007276 u, m_n = 1.008665 u, mass of ⁴₂He = 4.001506 u
Find mass defect and binding energy.
Solution:
He has Z=2 (2 protons), N=2 (2 neutrons)
Total mass of constituents = 2(1.007276) + 2(1.008665) = 2.014552 + 2.017330 = 4.031882 u
Δm = 4.031882 − 4.001506 = 0.030376 u
BE = 0.030376 × 931.5 = 28.3 MeV
BE/A = 28.3/4 = 7.07 MeV/nucleon
Numerical 2 — Binding Energy:
If the mass defect of a nucleus is 0.2 u, find the binding energy in MeV and Joules.
Solution:
BE = 0.2 × 931.5 = 186.3 MeV
In Joules: BE = 186.3 × 1.6 × 10⁻¹³ = 2.98 × 10⁻¹¹ J
(1 MeV = 1.6 × 10⁻¹³ J)
If the mass defect of a nucleus is 0.2 u, find the binding energy in MeV and Joules.
Solution:
BE = 0.2 × 931.5 = 186.3 MeV
In Joules: BE = 186.3 × 1.6 × 10⁻¹³ = 2.98 × 10⁻¹¹ J
(1 MeV = 1.6 × 10⁻¹³ J)
🔥 AMU PYQ: 1 atomic mass unit (amu) is equivalent to:
(A) 931.5 eV (B) 931.5 keV (C) 931.5 MeV (D) 931.5 J
Ans: C (1 u = 931.5 MeV/c²)
(A) 931.5 eV (B) 931.5 keV (C) 931.5 MeV (D) 931.5 J
Ans: C (1 u = 931.5 MeV/c²)
8) Einstein's Mass-Energy Equivalence — E = mc²
Albert Einstein's famous equation E = mc² states that mass and energy are equivalent. Mass can be converted to energy and vice versa. The conversion factor is the speed of light squared (c² ≈ 9 × 10¹⁶ m²/s²) — a huge number! That's why even a tiny mass produces enormous energy.
E = m × c²
E = energy (joules, J)
m = mass (kg)
c = speed of light (3 × 10⁸ m/s)
Proof that 1 u = 931.5 MeV:
1 u = 1.66 × 10⁻²⁷ kg
E = (1.66 × 10⁻²⁷)(3 × 10⁸)² = 1.494 × 10⁻¹⁰ J
1 MeV = 1.6 × 10⁻¹³ J
So 1 u = 1.494 × 10⁻¹⁰ / 1.6 × 10⁻¹³ = 931.5 MeV
🟡 This equation explains:
• Why nuclear reactions release so much energy (small mass loss → huge energy)
• The source of the Sun's energy (fusion of hydrogen → 4 million tons of mass converted to energy every second!)
• Why nuclear weapons are so devastating
• Mass defect → binding energy in nuclei
• Why nuclear reactions release so much energy (small mass loss → huge energy)
• The source of the Sun's energy (fusion of hydrogen → 4 million tons of mass converted to energy every second!)
• Why nuclear weapons are so devastating
• Mass defect → binding energy in nuclei
🔥 AMU PYQ: The energy released in nuclear reactions is governed by:
(A) E = ½mv² (B) E = mc² (C) E = mgh (D) E = hf
Ans: B (Einstein's mass-energy equivalence)
(A) E = ½mv² (B) E = mc² (C) E = mgh (D) E = hf
Ans: B (Einstein's mass-energy equivalence)
9) Nuclear Fission ⭐⭐
Nuclear fission is the splitting of a heavy nucleus into two (or more) lighter nuclei, accompanied by the release of neutrons and a large amount of energy.
Fission of Uranium-235:
Discovered by: Otto Hahn and Fritz Strassmann (1938). Explained by Lise Meitner and Otto Frisch.
²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3¹₀n + energy
Discovered by: Otto Hahn and Fritz Strassmann (1938). Explained by Lise Meitner and Otto Frisch.
Chain Reaction:
The 3 neutrons released in each fission can strike other U-235 nuclei, causing more fissions → each releases more neutrons → cascade. This is called a chain reaction.
🟡 Types of Chain Reaction:
1. Controlled chain reaction: The number of fissions is kept constant by absorbing some neutrons. Used in nuclear reactors for electricity generation
2. Uncontrolled chain reaction: The number of fissions grows exponentially (doubles every ~10⁻⁸ s). Releases enormous energy in a fraction of a second. Used in atom bombs
Critical mass: The minimum mass of fissile material required to sustain a chain reaction. For U-235, it's about 15-50 kg depending on geometry.
1. Controlled chain reaction: The number of fissions is kept constant by absorbing some neutrons. Used in nuclear reactors for electricity generation
2. Uncontrolled chain reaction: The number of fissions grows exponentially (doubles every ~10⁻⁸ s). Releases enormous energy in a fraction of a second. Used in atom bombs
Critical mass: The minimum mass of fissile material required to sustain a chain reaction. For U-235, it's about 15-50 kg depending on geometry.
Energy released in one fission:
~200 MeV per U-235 fission
1 kg of U-235 → energy equivalent to ~3000 tons of coal (~3 × 10¹³ J)!
~200 MeV per U-235 fission
1 kg of U-235 → energy equivalent to ~3000 tons of coal (~3 × 10¹³ J)!
Nuclear Reactor — Components and Working:
| Component | Function | Example Materials |
|---|---|---|
| Fuel | Fissile material that undergoes fission | Uranium-235 (3-5% enriched), Plutonium-239, Thorium-232 (in some reactors) |
| Moderator | Slows down fast neutrons to thermal speeds (so they can cause further fission) | Graphite, Heavy water (D₂O), Ordinary water (H₂O) |
| Control Rods | Absorb excess neutrons to control the reaction rate (can be raised/lowered) | Boron (B), Cadmium (Cd), Hafnium (Hf) |
| Coolant | Removes heat from the reactor core → used to produce steam → drives turbine | Water, Liquid sodium, Heavy water, CO₂ gas |
| Shielding | Protects workers/environment from radiation | Thick concrete walls (1-2 m), Lead lining |
Working of a Nuclear Reactor (simplified):
1. U-235 fuel rods fission → produce heat + fast neutrons
2. Moderator slows down neutrons → they cause more fission → sustained chain reaction
3. Control rods are adjusted to keep the reaction rate steady
4. Coolant circulates through the core → carries heat away
5. Heat is used to produce steam → steam drives turbine → generator → electricity
6. Concrete shielding absorbs radiation
1. U-235 fuel rods fission → produce heat + fast neutrons
2. Moderator slows down neutrons → they cause more fission → sustained chain reaction
3. Control rods are adjusted to keep the reaction rate steady
4. Coolant circulates through the core → carries heat away
5. Heat is used to produce steam → steam drives turbine → generator → electricity
6. Concrete shielding absorbs radiation
🟡 Nuclear Power Plants in India:
• Tarapur (Maharashtra) — India's first (1969)
• Kudankulam (Tamil Nadu) — Largest, 2×1000 MW (Russian VVER reactors)
• Kaiga (Karnataka)
• Rawatbhata (Rajasthan)
• Kalpakkam (Tamil Nadu) — Includes fast breeder reactor
• Kakrapar (Gujarat)
• Narora (Uttar Pradesh)
India has ~6.8 GW nuclear capacity, targeting ~22 GW by 2031
• Tarapur (Maharashtra) — India's first (1969)
• Kudankulam (Tamil Nadu) — Largest, 2×1000 MW (Russian VVER reactors)
• Kaiga (Karnataka)
• Rawatbhata (Rajasthan)
• Kalpakkam (Tamil Nadu) — Includes fast breeder reactor
• Kakrapar (Gujarat)
• Narora (Uttar Pradesh)
India has ~6.8 GW nuclear capacity, targeting ~22 GW by 2031
🔥 AMU PYQ: The function of a moderator in a nuclear reactor is to:
(A) Absorb neutrons (B) Slow down neutrons (C) Produce neutrons (D) Cool the reactor
Ans: B (moderator slows down fast neutrons to thermal energies)
(A) Absorb neutrons (B) Slow down neutrons (C) Produce neutrons (D) Cool the reactor
Ans: B (moderator slows down fast neutrons to thermal energies)
🔥 AMU PYQ: Cadmium rods are used in nuclear reactors as:
(A) Fuel (B) Moderator (C) Control rods (D) Coolant
Ans: C (control rods absorb excess neutrons)
(A) Fuel (B) Moderator (C) Control rods (D) Coolant
Ans: C (control rods absorb excess neutrons)
🔥 AMU PYQ: The most suitable moderator in a nuclear reactor is:
(A) Boron (B) Cadmium (C) Heavy water (D) Uranium
Ans: C (heavy water D₂O is an excellent moderator)
(A) Boron (B) Cadmium (C) Heavy water (D) Uranium
Ans: C (heavy water D₂O is an excellent moderator)
10) Nuclear Fusion ⭐⭐
Nuclear fusion is the process of combining two light nuclei to form a heavier nucleus, releasing enormous energy. This is the source of the Sun's energy and the most energetic process known.
Fusion Reaction Example (Deuterium-Tritium):
Proton-Proton Chain (Sun's core):
4¹₁H → ⁴₂He + 2β⁺ + 2νₑ + 26.7 MeV
(4 hydrogen nuclei combine to form 1 helium nucleus)
²₁H (D) + ³₁H (T) → ⁴₂He + ¹₀n + 17.6 MeV
Proton-Proton Chain (Sun's core):
4¹₁H → ⁴₂He + 2β⁺ + 2νₑ + 26.7 MeV
(4 hydrogen nuclei combine to form 1 helium nucleus)
🟡 Conditions for Fusion:
• Very high temperature (~10⁷ to 10⁸ K) to overcome electrostatic repulsion between positive nuclei
• Very high pressure (to bring nuclei close enough for nuclear forces to act)
• These conditions exist naturally in the Sun's core (~15 million K, ~250 billion atm)
• On Earth, they are achieved in a hydrogen bomb (using a fission trigger) and in experimental reactors (tokamak)
• Very high temperature (~10⁷ to 10⁸ K) to overcome electrostatic repulsion between positive nuclei
• Very high pressure (to bring nuclei close enough for nuclear forces to act)
• These conditions exist naturally in the Sun's core (~15 million K, ~250 billion atm)
• On Earth, they are achieved in a hydrogen bomb (using a fission trigger) and in experimental reactors (tokamak)
Fusion vs Fission — COMPARISON TABLE:
| Property | Nuclear Fission | Nuclear Fusion |
|---|---|---|
| Definition | Splitting a heavy nucleus into lighter ones | Joining two light nuclei to form a heavier one |
| Energy released | ~200 MeV per fission | ~3-24 MeV per fusion (but per unit mass, fusion releases more!) |
| Fuel | Uranium-235, Plutonium-239 (rare, expensive) | Hydrogen isotopes (D, T) — abundant (from water) |
| Conditions | Room temperature (neutron initiates fission) | Extremely high T and P (millions of degrees) |
| Chain reaction | Possible — self-sustaining | Very difficult to sustain — still experimental |
| Waste | Highly radioactive, long-lived waste | Relatively clean (He-4 is harmless) |
| Chernobyl/Fukushima risk | Yes — meltdown possible | No — reaction stops if containment fails |
| Weapons | Atom bomb (Nagasaki, Hiroshima) | Hydrogen bomb (thermonuclear — uses fission trigger) |
| Current use | Nuclear power plants (commercial) | Experimental (ITER tokamak, NIF laser fusion) |
| Sun's energy | NOT fission (Sun is not a nuclear reactor!) | YES — fusion of H to He |
🟡 Challenges of Fusion on Earth:
• Containment: No material can withstand millions of degrees. Solution: magnetic confinement (tokamak — uses strong magnetic fields to hold plasma)
• Plasma stability: The superheated plasma (ionized gas) is unstable and tends to escape
• Energy breakeven: So far, more energy is used to create the fusion conditions than is produced. The goal is Q > 1 (net energy gain), achieved in 2022 at NIF (Q ≈ 1.5)
• ITER: International Thermonuclear Experimental Reactor (France) — the world's largest fusion experiment, aiming for Q = 10 by 2035
• Containment: No material can withstand millions of degrees. Solution: magnetic confinement (tokamak — uses strong magnetic fields to hold plasma)
• Plasma stability: The superheated plasma (ionized gas) is unstable and tends to escape
• Energy breakeven: So far, more energy is used to create the fusion conditions than is produced. The goal is Q > 1 (net energy gain), achieved in 2022 at NIF (Q ≈ 1.5)
• ITER: International Thermonuclear Experimental Reactor (France) — the world's largest fusion experiment, aiming for Q = 10 by 2035
🔥 AMU PYQ: The source of energy in the Sun is:
(A) Nuclear fission (B) Nuclear fusion (C) Chemical reaction (D) Gravitational contraction
Ans: B (nuclear fusion of hydrogen into helium)
(A) Nuclear fission (B) Nuclear fusion (C) Chemical reaction (D) Gravitational contraction
Ans: B (nuclear fusion of hydrogen into helium)
🔥 AMU PYQ: In a hydrogen bomb, the reaction used is:
(A) Fission (B) Fusion (C) Both (D) Chemical
Ans: B (hydrogen bomb = fusion = thermonuclear)
(A) Fission (B) Fusion (C) Both (D) Chemical
Ans: B (hydrogen bomb = fusion = thermonuclear)
11) Applications of Radioactivity ⭐
Radioactivity has numerous beneficial applications across medicine, agriculture, industry, and research.
Medical Applications:
- Cobalt-60 (Co-60): Gamma rays destroy cancer cells — used in radiotherapy / teletherapy machines. This is the most common application
- Iodine-131 (I-131): Used for thyroid diagnosis and treatment. The thyroid gland naturally absorbs iodine, so I-131 concentrates there. Its radiation destroys overactive thyroid tissue (hyperthyroidism) or thyroid cancer. Also used as a tracer for imaging
- Technetium-99m (Tc-99m): The most widely used medical radioisotope. Used in SPECT scans for imaging bones, heart, lungs, kidneys, brain. Short half-life (6 hours) reduces patient radiation dose
- Sodium-24: Tracer to detect blood circulation problems
- Sterilization: Gamma rays (Co-60) sterilize medical equipment (syringes, bandages, surgical instruments) without heat or chemicals
Carbon Dating (Archaeology):
Carbon-14 Dating:
• C-14 is a radioactive isotope of carbon with half-life = 5730 years
• Formed continuously in the atmosphere (cosmic rays + N₂ → C-14)
• Plants absorb C-14 through photosynthesis → animals eat plants → all living things have the same C-14/C-12 ratio
• When an organism dies, it stops absorbing carbon → C-14 decays (C-14/C-12 ratio decreases)
• By measuring the remaining C-14/C-12 ratio, we can determine how long ago the organism died
• Effective range: up to ~50,000 years (older than that, too little C-14 remains)
• Used for: fossils, wood, bones, archaeological artefacts, Dead Sea Scrolls, Egyptian mummies
• C-14 is a radioactive isotope of carbon with half-life = 5730 years
• Formed continuously in the atmosphere (cosmic rays + N₂ → C-14)
• Plants absorb C-14 through photosynthesis → animals eat plants → all living things have the same C-14/C-12 ratio
• When an organism dies, it stops absorbing carbon → C-14 decays (C-14/C-12 ratio decreases)
• By measuring the remaining C-14/C-12 ratio, we can determine how long ago the organism died
• Effective range: up to ~50,000 years (older than that, too little C-14 remains)
• Used for: fossils, wood, bones, archaeological artefacts, Dead Sea Scrolls, Egyptian mummies
Agricultural Applications:
- Pest control: Gamma rays sterilize male insects → released into wild → no offspring → pest population declines (Sterile Insect Technique)
- Food preservation: Gamma irradiation kills bacteria, insects, and parasites → extends shelf life of food. Safe — food does NOT become radioactive
- Crop improvement: Radiation induces mutations in seeds → develop new varieties with higher yield, disease resistance, better nutrition (mutation breeding)
- Fertilizer tracer: P-32 (radioactive phosphorus) helps study how plants absorb fertilizer, optimizing usage
Industrial Applications:
- Thickness gauging: Beta or gamma rays passed through paper/plastic/metal sheets. The amount absorbed tells the thickness → automatic quality control in factories
- Radiography / NDT: Gamma rays (Ir-192, Co-60) used to detect cracks or defects in metal welds, pipes, pressure vessels (like X-rays for industrial parts)
- Leak detection: A small amount of radioactive tracer is added to a pipeline → detecting the radiation outside reveals leaks
- Smoke detectors: Contain Americium-241 (α source). α particles ionize the air → current flows. Smoke absorbs α particles → current drops → alarm triggers
🔥 AMU PYQ: Which isotope is used in cancer treatment?
(A) Uranium-235 (B) Cobalt-60 (C) Carbon-14 (D) Iodine-131
Ans: B (Cobalt-60 emits gamma rays used in radiotherapy)
(A) Uranium-235 (B) Cobalt-60 (C) Carbon-14 (D) Iodine-131
Ans: B (Cobalt-60 emits gamma rays used in radiotherapy)
🔥 AMU PYQ: Carbon-14 dating is used to determine:
(A) Age of rocks (B) Age of fossils (C) Speed of light (D) Temperature
Ans: B (carbon dating for fossils/organic matter up to ~50,000 years)
(A) Age of rocks (B) Age of fossils (C) Speed of light (D) Temperature
Ans: B (carbon dating for fossils/organic matter up to ~50,000 years)
🔥 AMU PYQ: Which isotope is used in thyroid treatment?
(A) Co-60 (B) I-131 (C) C-14 (D) Am-241
Ans: B (Iodine-131 for thyroid diagnosis and treatment)
(A) Co-60 (B) I-131 (C) C-14 (D) Am-241
Ans: B (Iodine-131 for thyroid diagnosis and treatment)
12) Radiation Hazards and Safety — NEW
While radioactivity has many beneficial uses, radiation can be harmful to living organisms. It damages cells by ionizing atoms in molecules (especially DNA), which can cause cancer, genetic mutations, and radiation sickness.
🟡 Biological Effects of Radiation:
• Acute effects: High dose in short time → radiation sickness (nausea, hair loss, burns, death). Symptoms appear within hours/weeks. LD50/30 = ~4-5 Sv (lethal dose for 50% of people within 30 days)
• Chronic effects: Low dose over long time → increased cancer risk, genetic mutations (birth defects in future generations)
• Background radiation: We are all exposed to natural radiation (~2-3 mSv/year from cosmic rays, radon gas, food, medical X-rays)
• ALARA Principle: As Low As Reasonably Achievable — minimize radiation exposure
• Acute effects: High dose in short time → radiation sickness (nausea, hair loss, burns, death). Symptoms appear within hours/weeks. LD50/30 = ~4-5 Sv (lethal dose for 50% of people within 30 days)
• Chronic effects: Low dose over long time → increased cancer risk, genetic mutations (birth defects in future generations)
• Background radiation: We are all exposed to natural radiation (~2-3 mSv/year from cosmic rays, radon gas, food, medical X-rays)
• ALARA Principle: As Low As Reasonably Achievable — minimize radiation exposure
Radiation Safety Measures:
- Time: Minimize time spent near radiation sources
- Distance: Stay as far away as possible (intensity follows inverse square law)
- Shielding: Use appropriate barriers — α (paper), β (aluminum), γ (lead/concrete)
- Monitoring: Use radiation badges (film badges, Geiger-Müller counters, dosimeters) to track exposure
- Containment: Radioactive materials stored in lead-lined containers, handled with remote tools in hot cells
- Waste disposal: Low-level waste → shallow burial. High-level waste (spent fuel) → stored in cooling pools, then deep geological repositories
13) PYQ Battle — AMU Past Questions on Nuclear Physics
🔥 Q1. Which of the following is NOT a type of radioactive radiation?
(A) Alpha (B) Beta (C) Gamma (D) Delta
Ans: D
(A) Alpha (B) Beta (C) Gamma (D) Delta
Ans: D
🔥 Q2. Alpha particles are:
(A) Electrons (B) Protons (C) Helium nuclei (D) Neutrons
Ans: C
(A) Electrons (B) Protons (C) Helium nuclei (D) Neutrons
Ans: C
🔥 Q3. Cadmium rods are used in nuclear reactors as:
(A) Fuel (B) Moderator (C) Control rods (D) Coolant
Ans: C
(A) Fuel (B) Moderator (C) Control rods (D) Coolant
Ans: C
🔥 Q4. The energy released in nuclear reactions is governed by:
(A) E = ½mv² (B) E = mc² (C) E = mgh (D) E = hf
Ans: B
(A) E = ½mv² (B) E = mc² (C) E = mgh (D) E = hf
Ans: B
🔥 Q5. In a hydrogen bomb, the reaction used is:
(A) Fission (B) Fusion (C) Both (D) Chemical
Ans: B
(A) Fission (B) Fusion (C) Both (D) Chemical
Ans: B
🔥 Q6. The half-life of a radioactive sample is 10 days. After 30 days, the remaining fraction is:
Ans: (½)³ = 1/8
Ans: (½)³ = 1/8
🔥 Q7. Carbon-14 dating is used to determine:
(A) Age of rocks (B) Age of fossils (C) Speed of light (D) Temperature
Ans: B
(A) Age of rocks (B) Age of fossils (C) Speed of light (D) Temperature
Ans: B
🔥 Q8. Which radiation is deflected towards the positive plate in an electric field?
(A) Alpha (B) Beta (C) Gamma (D) None
Ans: B (beta = electron, −ve charge → attracted to +ve plate)
(A) Alpha (B) Beta (C) Gamma (D) None
Ans: B (beta = electron, −ve charge → attracted to +ve plate)
🔥 Q9. The most suitable moderator in a nuclear reactor is:
(A) Boron (B) Cadmium (C) Heavy water (D) Uranium
Ans: C
(A) Boron (B) Cadmium (C) Heavy water (D) Uranium
Ans: C
🔥 Q10. The energy in the Sun is produced by:
(A) Fission of uranium (B) Fusion of hydrogen (C) Burning of coal (D) Chemical reactions
Ans: B
(A) Fission of uranium (B) Fusion of hydrogen (C) Burning of coal (D) Chemical reactions
Ans: B
🔥 Q11. β-particles are:
(A) Helium nuclei (B) Fast electrons (C) EM waves (D) Protons
Ans: B (β⁻ are fast electrons)
(A) Helium nuclei (B) Fast electrons (C) EM waves (D) Protons
Ans: B (β⁻ are fast electrons)
🔥 Q12. The SI unit of radioactivity is:
(A) Becquerel (B) Curie (C) Rutherford (D) Roentgen
Ans: A (Becquerel, Bq. 1 Bq = 1 disintegration/s. Also Curie: 1 Ci = 3.7×10¹⁰ Bq)
(A) Becquerel (B) Curie (C) Rutherford (D) Roentgen
Ans: A (Becquerel, Bq. 1 Bq = 1 disintegration/s. Also Curie: 1 Ci = 3.7×10¹⁰ Bq)
🔥 Q13. Which radiation is NOT deflected by a magnetic field?
(A) Alpha (B) Beta (C) Gamma (D) Both A and B
Ans: C (gamma has no charge → no magnetic deflection)
(A) Alpha (B) Beta (C) Gamma (D) Both A and B
Ans: C (gamma has no charge → no magnetic deflection)
🔥 Q14. In α-decay, the mass number of the daughter nucleus:
(A) Increases by 4 (B) Decreases by 4 (C) Remains same (D) Increases by 2
Ans: B (A decreases by 4, Z decreases by 2)
(A) Increases by 4 (B) Decreases by 4 (C) Remains same (D) Increases by 2
Ans: B (A decreases by 4, Z decreases by 2)
🔥 Q15. The most stable nucleus in terms of binding energy per nucleon is:
(A) Uranium-235 (B) Helium-4 (C) Iron-56 (D) Carbon-12
Ans: C (Fe-56 has the highest BE/A ~8.8 MeV/nucleon)
(A) Uranium-235 (B) Helium-4 (C) Iron-56 (D) Carbon-12
Ans: C (Fe-56 has the highest BE/A ~8.8 MeV/nucleon)
🔥 Q16. The mass of an atom is always _____ the sum of masses of its constituents.
(A) Equal to (B) Less than (C) Greater than (D) Unrelated to
Ans: B (mass defect — the missing mass is converted to binding energy)
(A) Equal to (B) Less than (C) Greater than (D) Unrelated to
Ans: B (mass defect — the missing mass is converted to binding energy)
🔥 Q17. Lenz's law is related to the conservation of:
(A) Energy (B) Charge (C) Momentum (D) Mass
Ans: A (Wait — Lenz's law is about induced current opposing change, which conserves energy. But in nuclear physics, this question is usually about Soddy-Fajans or general conservation)
(A) Energy (B) Charge (C) Momentum (D) Mass
Ans: A (Wait — Lenz's law is about induced current opposing change, which conserves energy. But in nuclear physics, this question is usually about Soddy-Fajans or general conservation)
🔥 Q18. The half-life of C-14 is:
(A) 573 years (B) 5730 years (C) 57300 years (D) 57.3 years
Ans: B (5730 years)
(A) 573 years (B) 5730 years (C) 57300 years (D) 57.3 years
Ans: B (5730 years)
🔥 Q19. Which of the following is used as a coolant in nuclear reactors?
(A) Graphite (B) Liquid sodium (C) Cadmium (D) Boron
Ans: B (liquid sodium is used as coolant in fast breeder reactors)
(A) Graphite (B) Liquid sodium (C) Cadmium (D) Boron
Ans: B (liquid sodium is used as coolant in fast breeder reactors)
🔥 Q20. Nuclear fission was discovered by:
(A) Rutherford (B) Becquerel (C) Hahn and Strassmann (D) Fermi
Ans: C (Otto Hahn and Fritz Strassmann, 1938)
(A) Rutherford (B) Becquerel (C) Hahn and Strassmann (D) Fermi
Ans: C (Otto Hahn and Fritz Strassmann, 1938)
14) Common Mistakes — DON'T DO THESE!
🟡 Senior's Warning — Top 10 Mistakes:
1. ❌ Confusing fission and fusion: Fission = SPLITTING (heavy → light). Fusion = JOINING (light → heavy). The Sun does fusion, NOT fission
2. ❌ α, β, γ penetration order: γ (most penetrating) > β > α (least). But ionizing power is REVERSE: α (most ionizing) > β > γ (least)
3. ❌ Half-life formula errors: N = N₀ × (½)ⁿ where n = t/T₁/₂. Common mistake: n = T₁/₂/t (inverted!)
4. ❌ Binding energy per nucleon vs total: BE/A (per nucleon) tells stability. Total BE (Δm·c²) is the total energy holding the nucleus. Fe-56 has highest BE/A, not highest total BE
5. ❌ Mass defect direction: Mass of nucleus is LESS than sum of constituents (missing mass = energy). It's NOT more!
6. ❌ 1 u = 931.5 MeV (not eV or keV): This is a very common MCQ. Remember: 1 u = 931.5 MeV/c²
7. ❌ α-decay changes A and Z; β-decay changes only Z: α: A−4, Z−2. β⁻: A same, Z+1. β⁺: A same, Z−1. γ: no change
8. ❌ Control rods vs Moderator: Control rods ABSORB neutrons (Boron, Cadmium). Moderator SLOWS neutrons (Graphite, Heavy water). Different functions!
9. ❌ Atom bomb vs Hydrogen bomb: Atom bomb = fission. Hydrogen bomb = fusion (uses fission as trigger). H-bomb is more powerful
10. ❌ Carbon dating range: C-14 dating works only up to ~50,000 years (about 9 half-lives). After that, too little C-14 remains to measure accurately. It does NOT work for dinosaur fossils (millions of years old)
1. ❌ Confusing fission and fusion: Fission = SPLITTING (heavy → light). Fusion = JOINING (light → heavy). The Sun does fusion, NOT fission
2. ❌ α, β, γ penetration order: γ (most penetrating) > β > α (least). But ionizing power is REVERSE: α (most ionizing) > β > γ (least)
3. ❌ Half-life formula errors: N = N₀ × (½)ⁿ where n = t/T₁/₂. Common mistake: n = T₁/₂/t (inverted!)
4. ❌ Binding energy per nucleon vs total: BE/A (per nucleon) tells stability. Total BE (Δm·c²) is the total energy holding the nucleus. Fe-56 has highest BE/A, not highest total BE
5. ❌ Mass defect direction: Mass of nucleus is LESS than sum of constituents (missing mass = energy). It's NOT more!
6. ❌ 1 u = 931.5 MeV (not eV or keV): This is a very common MCQ. Remember: 1 u = 931.5 MeV/c²
7. ❌ α-decay changes A and Z; β-decay changes only Z: α: A−4, Z−2. β⁻: A same, Z+1. β⁺: A same, Z−1. γ: no change
8. ❌ Control rods vs Moderator: Control rods ABSORB neutrons (Boron, Cadmium). Moderator SLOWS neutrons (Graphite, Heavy water). Different functions!
9. ❌ Atom bomb vs Hydrogen bomb: Atom bomb = fission. Hydrogen bomb = fusion (uses fission as trigger). H-bomb is more powerful
10. ❌ Carbon dating range: C-14 dating works only up to ~50,000 years (about 9 half-lives). After that, too little C-14 remains to measure accurately. It does NOT work for dinosaur fossils (millions of years old)
15) Quick Revision — One-Liner Summary
| Topic | Key Point |
|---|---|
| Nucleus Discovery | Rutherford (1911) — gold foil α-scattering experiment |
| Nucleus Composition | Protons + Neutrons = Nucleons. Z = p⁺, A = p⁺+n⁰ |
| Nuclear Size | ~10⁻¹⁵ m. Density ~2.3×10¹⁷ kg/m³ (independent of A) |
| Radioactivity | Becquerel (1896). Spontaneous emission from unstable nuclei |
| α-particles | ⁴₂He²⁺, +2e, mass 4u, most ionising, stopped by paper |
| β-particles | ₋₁⁰e⁻ (electron), −1e, stopped by 5mm Al, moderate ionising |
| γ-rays | EM wave, 0 charge, speed of light, most penetrating, thick lead |
| α-decay | A−4, Z−2 (Soddy-Fajans). Example: ²³⁸U → ²³⁴Th + α |
| β-decay | A same, Z+1. Example: ²³⁴Th → ²³⁴Pa + β⁻ |
| Half-Life | T₁/₂ = 0.693/λ. N = N₀ × (½)ⁿ, n = t/T₁/₂ |
| Mass Defect | Δm = Σm_constituents − M_nucleus (always positive) |
| Binding Energy | BE = Δm·c². 1 u = 931.5 MeV. Fe-56 has max BE/A (8.8 MeV) |
| E = mc² | Einstein: mass & energy equivalent. Small mass → huge energy |
| Nuclear Fission | Heavy splits (U-235 + n → Ba + Kr + 3n + ~200 MeV) |
| Chain Reaction | Controlled (reactor) vs Uncontrolled (bomb). Critical mass |
| Nuclear Reactor | Fuel (U-235), Moderator (graphite/D₂O), Control rods (B/Cd), Coolant, Shielding |
| Nuclear Fusion | Light nuclei combine (²H+³H → ⁴He+n+17.6 MeV). Sun's energy |
| Applications | Co-60 (cancer), I-131 (thyroid), C-14 (fossil dating), Tc-99m (imaging), smoke detectors (Am-241) |
| Radiation Safety | Time, Distance, Shielding (ALARA principle). Lead/concrete for γ |
🟡 Final Senior's Message — The Complete Picture:
✅ Nuclear Physics marks the end of your AMU 11 Science Physics preparation! This chapter is small but important — master the α-β-γ table, half-life formula, fission vs fusion, and you'll get the question right.
Key to success in AMU Physics:
① Electricity (3-4 Qs) — Ohm's law, series/parallel, power formulas
② Magnetic Effect (1-2 Qs) — Fleming's rules, motor/generator
③ Sources of Energy (1 Q) — classification, one fact per source
④ Nuclear Physics (1 Q) — α-β-γ table, fission/fusion
You've got this! All the best for AMU 11 Science! 💪✨
✅ Nuclear Physics marks the end of your AMU 11 Science Physics preparation! This chapter is small but important — master the α-β-γ table, half-life formula, fission vs fusion, and you'll get the question right.
Key to success in AMU Physics:
① Electricity (3-4 Qs) — Ohm's law, series/parallel, power formulas
② Magnetic Effect (1-2 Qs) — Fleming's rules, motor/generator
③ Sources of Energy (1 Q) — classification, one fact per source
④ Nuclear Physics (1 Q) — α-β-γ table, fission/fusion
You've got this! All the best for AMU 11 Science! 💪✨
✅ Nuclear Physics — DONE! 🎉 All four chapters complete. You're fully prepared for AMU 11 Science Physics!